The World Health Organization (2020) defines obesity as the accumulation of abnormal or excessive fat that may negatively impact health. A simple index of weight-for-height, known as body mass index (BMI), is commonly used in the classification of overweight and obesity and refers to a person’s weight (in kilograms) divided by the square of his or her height in meters (kg/m2). Obesity continues to be a global public health concern. In 2016, 39% of adults aged 18 and above were overweight while 13% were obese; this translates to a total of 1.9 billion overweight adults and more than 650 million obese adults living during that year. (WHO 2020)
The rise in obesity also impacts the prevalence of the following obesity-related diseases and conditions:
- Coronary heart disease (Engin 2017)
- Cancer (Engin 2017)
- Type 2 diabetes (Engin 2017)
- Dyslipidemia (Nejat 2010)
- Hypertension (Nejat 2010)
- Venous thrombosis (Nejat 2010)
- Depression (Nejat 2010)
- Metabolic syndrome (National Heart, Lung, and Blood Institute n.d.)
- Atherosclerosis (National Heart, Lung, and Blood Institute n.d.)
- Sleep disorders (National Heart, Lung, and Blood Institute n.d.)
- Chronic liver disease (Sarwar 2018)
- Orthopedic risk (eg: arthritis) (Niemiro 2020)
- Heart failure, specifically for heart failure with preserved ejection fraction (HFpEF) (Carbone 2020)
- Decreased fertility and increased risk for gestational diabetes, hypertensive disease during pregnancy, fetal growth abnormalities, and congenital anomalies (Chandrasekaran & Neal-Perry 2017)
Prevalence and Risk Factors of Obesity
The pathogenesis of obesity is quite complex with causation and persistence resulting from numerous factors to include (Gadde 2018 and Tsegaye 2020):
Clinical Interventions for Obesity
There are various types of treatments used in the management of obesity including behavioral, pharmacological, and surgical interventions. It is advised that behaviorally-based interventions be the first option considered in the treatment of obesity. Additionally, even with medical interventions, it is still recommended to continue implementing changes in dietary and physical activity behaviors for continued weight loss or maintenance of weight loss. The primary goal of behavioral modification programs is to modify energy-balance behaviors so as to improve weight status, mainly by focusing on increasing energy expenditure and reducing energy intake. (Wilfley 2018)
There are a variety of pharmacological interventions used in the management of obesity including, but not limited to, the following medications:
- Phentermine
- Topiramate
- Orlistat
- Lorcaserin
- Liraglutide
- Bupropion/naltrexone
- Lisdexamfetamine dimesylate
- Exenatide
- Zonisamide
Bariatric surgery refers to surgery that is used for weight loss and, thus, in the treatment and management of obesity. The three types of operations most commonly used for bariatric surgery include the vertical sleeve gastrectomy (VSG), Roux-en-Y gastric bypass (RYGB), and the adjustable gastric banding (ABG). (Albaugh & Abumrad 2018)
Individual weight loss resulting from each of the aforementioned treatments for obesity is highly variable, with multiple factors potentially contributing to this inter-individual response variability; these factors include (Dent 2020):
- Heritability
- Adherence to treatments
- Under-reporting of food intake while over-reporting physical activity
- T3 and T4 levels
- Macronutrient composition of diets
- Inter-individual variability in response to non-exercise activity thermogenesis (NEAT)
- Response to medications
- Age
- Gender
- Microbiome (eg: Prevotella-enterotype vs Bacteroides-enterotype)
The Effect of Obesity on Exercise Performance
Individuals who are obese have compromised cardiorespiratory fitness and physiologic function which is impacted by skeletal muscle dysfunction and other aerobic exercise testing variables (Arena & Cahalin 2014). Evidence also suggests that inspiratory and expiratory respiratory muscle function is potentially impaired as a direct consequence of obesity which, in turn, may exacerbate exertional symptoms as well as compound the limitations in cardiorespiratory fitness (Arena & Chain 2014). Excessive body fat subjects the heart to an unfavorable burden and hinders cardiac function, especially during intense exercise (Setty 2013). Additionally, VO2max is substantially decreased in overweight persons when fat mass is considered (Setty 2013).
Individuals who are obese tend to manifest various aerobic exercise test abnormalities and diminished responses due to their body habitus. Obese individuals have also been found to have endothelial dysfunction, experiencing lower flow mediated dilation values compared to their lean counterparts. Biomechanical abnormalities, such as altered gait patterns, that are commonly associated with obesity also contribute to abnormal responses to exercise. Additionally, biomechanical inefficiency and/or orthopedic pain mainly contribute to limiting maximal effort during aerobic exercise. (Arena & Cahalin 2014)
Exercise Interventions for Obesity
Physical activity has been shown to be an important behavioral factor for both weight loss and prevention of weight gain, specifically following successful weight loss. Exercise increases energy expenditure, which causes a negative energy balance and thus contributes to weight loss, making it an effective strategy in fighting obesity (Petridou 2019). Evidence also suggests that exercise aids in reducing chronic, systemic inflammation which is common in obese individuals and increases the risk for various major diseases (You 2013).
Regular aerobic and resistance training increases cardiorespiratory and muscular fitness, respectively, resulting in improved body composition, enhanced bone health, improved cognitive function, and other such benefits (Garber 2019). Aerobic exercise, specifically, contributes to improvements in blood pressure, glucose intolerance, low-density lipoprotein and high-density lipoprotein levels, and inflammatory markers (Garber 2019). Resistance training, however, has been found to preferentially mobilize, and thus decrease, the visceral and subcutaneous adipose tissue in the abdominal region (Strasser 2011).
Exercise Guidelines for Obesity
The objectives of an exercise program in the treatment of obesity should be (in the following decreasing order of priority) to prevent additional weight gain, reduce body weight, and maintain (long-term) the reduction in body weight. It is important to note that the volume of exercise needed for weight loss is greater than the volume of exercise needed for improving fitness (McQueen 2009). Endurance exercise may be the most well-known and effective type of exercise for weight loss, due to its easy applicability to obese people while enabling high energy expenditure (Petridou 2019). However, resistance training as well as intermittent exercise also offer various and additional benefits and thus can also be incorporated into weight management programs (Petridou 2019). Initially, training intensity should be modest (40%-60% of VO2 reserve or heart rate reserve) and should take into account deconditioning while maintaining focus on duration and frequency rather than on intensity (McQueen 2009). Given that obese individuals have decreased cardiorespiratory fitness, are not experienced in exercise, and are at a high risk for musculoskeletal injuries as a result of excess body weight, it is important that exercise programs incorporate exercises that are safe and make the patient feel comfortable so as to ensure adherence to the exercise program. (Petridou 2019)
Dietary Interventions for Obesity
Dietary intervention is a key component of weight loss therapy, with energy content and macronutrient composition generally being the focus of the regimen (Fock & Khoo 2013). According to Capewell and Lloyd-Williams (2017), poor diet is responsible for a larger global burden of non-communicable disease than physical inactivity, tobacco, and alcohol combined. Generally speaking, there are four main types of dietary regimens that are used to treat overweight or obesity (Fock & Khoo 2013):
- Low-calorie diet (LCD)
- Low-fat diet
- Low-carbohydrate diet
- Very low-calorie diet (VLCD)
Other dietary patterns that have shown success with weight loss and may be beneficial when treating overweight or obesity include the following:
In addition to specific dietary patterns, other factors associated with weight loss are currently being investigated:
- Fiber and gut bacteria (Matusheski 2021)
- Fructose and appetite (Teff 2004)
- Meal frequency and timing (Cameron 2010, Lowe 2020)
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